An Introduction to Extended Riverfly

What is it and what is it for?

Extended Riverfly is intended for people who already have a few years’ experience in using RMI. They should already be familiar with the basic eight RMI target groups and have got know many of the other river invertebrate groups. Extended Riverfly is an expansion of the original RMI method that uses 33 invertebrate groups, including the basic eight RMI groups. It includes most of the major groups of macroinvertebrates you are likely to find in your samples and gives more nuanced idea of what is going on in the river than RMI; the river’s quality, possible stressors and its biodiversity. Rather than being a replacement for the monthly RMI sampling, Extended Riverfly is best used on a seasonal (especially spring and autumn) or annual basis to assess, for example, the performance of river restorations or the impacts of outfalls.

How does it work?

The Extended Riverfly sampling method is almost the same as RMI. It uses a 3-minute kick sample but also includes a 30-second surface sweep, to detect surface living insects such as pond skaters, water measurers and water crickets, and the stone search is reduced to 30 seconds. Sorting your sample for Extended Riverfly is likely to add at least an hour to the basic RMI sampling time. Links are available on the Riverfly Partnership website to various Extended Riverfly resources including the identification chart, the scoring system, and John Davy-Bowker’s You Tube video channel showing the sampling method and the invertebrate target groups.

Extended Riverfly includes several invertebrate groups that are tolerant of organic pollution, low flow and siltation. Large numbers of these will reflect the impacts of those stressors. There are four abundance classes, the same as in RMI, but the scoring system gives increasingly negative values to stress-tolerant taxa. Extended Riverfly produces two overall scores: a Water Quality Score (WQS) and a Silt and Flow Score (SFS), but you can also derive an RMI score from your sample too. These are all calculated when you upload your data onto the national Cartographer Riverfly database. There is no Trigger Level based on Extended Riverfly, trigger levels are still calculated from the RMI score.

Training

There is now a national network of qualified Extended Riverfly tutors who can provide training workshops in many areas of the UK. The training is an iterative process, typically comprising two or three sessions of tutored sorting of a sample, collected in a local river, to establish the consistency of potential monitors to identify the catch at different times of year. There is a test at the end of the workshop to identify a selection of 20-30 specimens. A 90% pass mark is required before monitors are signed off to upload data to national database, but everyone is encouraged to keep their own records before that.

What do the scores mean?

There are about 1300 Extended Riverfly records currently available on the National Riverfly Database from across the country. These data show WQS range from 0 to 52 and suggest poor scores are below 15 and scores indicating good water quality are above 35. Similarly, SFS scores below 15 indicate sites badly impacted by low flows and siltation, whereas scores above 40 indicate rivers not badly impacted by siltation or low flows.